This invention relates to offset printing presses, and more particularly to the removal of spray powder used to help dry the printed sheets. Some of the environmental problems associated with the spray powder in the atmosphere of a print shop are recognized and resolved.
The offset printing presses of the present time are relatively high speed machines meeting the practical requirements of high-production and quality-geared offset print shops. Some of the most sophisticated technology machines are made by Heidelberg Druckmaschinen Acktiengesellschaft of Heidelberg, Germany which uses sheet-fed offset printing. Such machines are referred to herein as "the Heidelberg". Sheets are printed at a rate of up to 12,000 sheets per hour. The requirements for transporting, printing, drying and stacking sheets are critical to achieve these fast printing speeds. The drying of the printing ink which has been applied to the individual sheets is very critical to delivering, discharging and stacking of sheets in the sheet discharge section. Problems using a spray powder on the printed sheets is the subject of this invention.
Systems for drying the printed sheets have been disclosed in U.S. Pat. Nos. 4,233,901 and 5,115,741. In U.S. Pat. No. 4,233,901 a chamber and a heater for producing a pressurized air flow to be directed onto the printed stock helps dry the stock. A further collector means for collecting the solvent mixture from the drying operation and mixing it with fresh air to recirculate through the chamber is provided. The invention of U.S. Pat. No. 5,115,741 includes a radiation device located outside the printing machine for generating radiant energy and a device to transmit this radiant energy to a surface of the printed product. An ultraviolet ink is used in the offset printing and this ink is cured by being exposed to ultraviolet light of the radiation device.
The commonly used drying means in the Heidelberg includes a spray powder device and a heater to keep the sheets from contacting one another in the stack until drying can be achieved. This spray of powder is normally introduced at the location of the sheet delivery and sheet discharge sections of the printing press. The particle size of the spray powder is sufficient to keep the ink film from transferring to the sheet above in a printed stack of sheets as the ink is drying. This allows the press to have a large stack of sheets at the sheet discharge section which are not marked. A light source is also used to electrostatically charge the spray powder particles causing them to be attracted toward the paper stock. However, not all the spray powder is used in the process and a considerable amount of powder is free in the air to penetrate other sections of the printing press as well as to exit the printing press. This free powder within the powder-laden air is trapped in cooling fans and motors, interferes with the proper lubrication of the printing press causing wear of the press parts, creates a dirty work space and is very slippery where it settles in one location. This powder-laden air can also affects the other operations of the printing company in addition to the print shop including the camera, stripping and plate rooms.
Powder spray and cleaning systems have been disclosed in U.S. Pat. Nos. 3,053,180 and 4,024,815. The system of U.S. Pat. No. 3,053,180 comprises a distributing and scavenging head structure associated with an anti-static bar to apply a spray powder to freshly printed paper and to remove all excess from the paper while preventing air transport of powder from the region of application. The head structure is contoured to fit closely to the transfer cylinders and to develop an air curtain to control the overspray of powder. The system of U.S. Pat. No. 4,024,815 is a combination spray and suction device. The device operates to spray powder in a controlled zone and to receive surplus powder by a vacuum system and return it for reuse. Once again, the system of this patent depends on providing a curtain of blast air which prevents the powder from escaping the control zone.
The control of the flow of laden air can be provided by physical barriers or devices such as those described in U.S. Pat. No. 3,410,070 and in the brochure entitled Air-O-Vac from Mechanical Air Purifiers, Inc. of Allentown, Pa. In the patent U.S. Pat. No. 3,410,070 the bobbin carriage of a textile manufacturing machine has a stream of air controlled by a flexible wall. The wall prevents an untimely release of the downward flow of air from nozzles to the outside of the machine. The flow of air eliminates "fly" in the area affected by air currents, and the air flow is exhausted without further treatment. The Air-O-Vac system incorporates a hood above the sheet delivery section of the Heidelberg for the powder-laden air that flows upward out of the sheet delivery section of the printing press. The upward movement of air is opposed to the downward movement of the sheets to reach the sheet discharge section, often resulting in sheet discharge and stacking problems. A filter bank with a motor and fan is alleged to remove 80 percent of the excess spray powder without paper flutter down to 60 lb. stock paper.
Removal of powder from powder-laden air by forcing the air through filters to collect the powder within the filter media can be an effective method. In U.S. Pat. No. 3,412,31 the removal of dirt from the air circulation system is by substantially tubular elements with straight walls which taper at their end. These elements are referred to in the present technology as "bag filters" which have a high average efficiency in the removal of particles from the air. For example, the Micro Air air cleaners manufactured by Metal-Fab, Inc. of Wichita, Kans. use an 8-pocket bag filter along with a pre-filter to achieve high average efficiency filters.
Present systems for removal of the powder from powder-laden air do not achieve the efficiency or effectiveness necessary for the printing press of the Heidelberg type. The need continues to remove powder from the powder-laden air below the sheet delivery section where the sheet discharge section is located. This section has powder-laden sheets in a vertical stack. The need exists to create an improved air flow direction within the sheet discharge section and to provide at least one exhaust vent properly located within the sheet discharge section.
Accordingly, an object of the present invention is to provide a system to remove the spray powder from the powder-laden air created by the printing press. In particular, the invention is to provide clean air to be exhausted back into the press shop without interferring with the delivery of the printed paper or without unduly consuming floor space.
Another object of the present invention is to help eliminate contaminates in the shop air that get into the printing press ink and cause the printed materials to be flawed.
Yet another object of the present invention is to provide a cleaner and healthier place to work and to cut down on the maintenance of the printing press equipment within the press room including the room air conditioning and heating systems. This object includes saving energy costs for heating and air conditioning the press shop by not exhausting the powder-laden air to the outside.